In preparing oil well boreholes for production, an important step is cementing a casing into place in the borehole. Primary cementing operations involved in preparing a new well for production include pumping a cement slurry down the steel casing and forcing it into the annulus between the casing and the borehole from the bottom of the well up toward the surface. Cementing a well protects and separates the various fluid producing zones from one another and protects the casing from corrosion. Cementing also lessens the danger of contaminating water supplies and helps prevent oil well blowouts and fires caused by underground high pressure zones.
During primary cementing operations, it is desirable that the outer periphery of the casing be cemented to the borehole wall along its entire length. When wells were relatively shallow, cementing was accomplished by pumping the cement slurry down the casing and back up the annulus between the casing and the borehole all the way to the surface of the well. However, in deep wells this method has proven to be unsatisfactory. As a result, a multiple stage cementing process was developed to allow the annulus to be cemented in separate stages, starting at the bottom of the well and progressing in stages up to the surface.
Multiple stage cementing is accomplished by the use of cementing tools, which are placed in the casing at one or more locations in the borehole. In the first stage of the cementing operation, cement is pumped to the bottom of the casing and up the annulus to the lowest cementing tool in the well. In the next stage of the operation, the lower portion of the casing string is closed off and cement is pumped through a valve in the cementing tool into the annulus and up to the next cementing tool in the well. Multiple stages of cementing are completed in this manner up to the surface of the well.
During primary cementing operations it is desirable that the casing string be rotated and/or reciprocated to enhance cement bonding between the casing and the borehole wall. If the casing is not rotated and/or reciprocated while the cement is being forced into the annulus, poor bonding is likely to result. During the first stage of cementing, the entire casing string can be rotated and/or reciprocated while the cement is pumped into the annulus. However, after the first stage of cementing is complete and the casing string is fixed in place, further rotation and/or reciprocation of the casing string generally becomes impossible. Thus, there is a need for a device which allows rotation and/or reciprocation of the upper casing string after the lower casing string has been cemented in place in a multiple stage cementing operation.